Electrode for electrical systems



July 29, 1952 R. s. DEAN ELECTRODE FOR ELECTRICAL SYSTEMS Filed Nov. 17,1950 (MEI/e3 i Mk2.

W E 5 W 4 m m m E V m Patented July 29, 1952 ELECTRODE FOR ELECTRICALSYSTEMS Reginald S.Dean, Washington, D. C., assignor to ChicagoDevelopment Corporation, Riverdale,

Md.,"a corporation of Delaware Application November 17, 1950, Serial No.196,177

This invention relates to electrodes for electrical systems. It relatesparticularly to such systems where it is desirable to have a highlyelectropositive material as an electrode. By an electropositive materialis meant one which has an electrode potential in solutions of its ionsnear that of the alkali metals. Such electropositive materials are alsocharacterized by a low work. function for the thermionic emission ofelectrons. In the known art these electropositive properties have beenfound only in alkali metals and in alloys of alkali metals which arerapidly attacked by water. The rapidity of such attack by water and themechanical and physical properties such as strength and melting pointhas prevented the practical use of these materials for many purposes forwhich they are, otherwise, well suited; for example, electrodes in wateractivated primary cells, electrodes in electronic discharge devices, andthe like. I have found that certain alloys of lithium and magnesiumpossess electropositive properties very close to those of lithium but atthe same time are far less reactive with water.

In the figure, curve I, I have illustrated the electrode potential of aseries of lithium-magnesium alloys measured against metallic lithium, Itwill be seen that up to 60% magnesium there is a small increase in thepotential against lithium amounting at 60% magnesium to less than 0.3volt. In curve 2, of the figure, I have illustrated the rate of attackof the alloy by water in arbitrary units. It will be seen that at 60%magnesium the rate of attack is very much less than that of lithium orof lithiummagnesium alloys with less than 50% magnesium. Consequently,in the range of 52-70% magnesium these alloys are within 0.8 volt aselectropositive as lithium and yet react much less rapidly with water.

As specific examples of the rate of reaction with water I give thefollowing:

Hydrogen evolution in water per unit surface Alloy 55% Magnesium 60%Magnesium 65% Magnesium 3 ;Claims. (Cl. 136-100) of this invention maybemade by methods known in the art. It is'convenient to make the-alloysby melting together the pure metals in an iron crucible fitted with athin steel diaphragm at the bottom below which is a suitable mold. The

crucible and the mold are contained in a casing which is maintained fullof argon. The whole is heated in a furnace until the metal is at atemperature of 800 C. It is then thoroughly stirred and the diaphragmpierced With a steel rod and the alloy allowed to flow into the mold.-

After cooling in the argon atmosphere the ingots are coated with oil androlled to the desired form.

I have found that the lithium-magnesium alloys are resistant to attackby air, being protected by a superficial coating. These alloys have beenkept for periods up to 6 months in air of 50% relative humidity and havebeen kept for an indefinite period of time in a dessicator withoutdamage.

Since the lithium-magnesium alloys may be readily rolled primary cellsmay be formed from them in any of the known ways for making such cellsfrom magnesium. For example, cells made using lithium-magnesium alloysas anode material and silver chloride on silver, as cathode and usingsea water as electrolyte showed the following discharge voltages at 0.8ampere per square inch. A magnesium-silver chloride cell according tothe known art is included for comtrolyte.

Similar advantages in discharge voltage are shown against otherdepolarizers including copper sulphate, manganese dioxide, and silverperoxide.

Cells using the lithium-magnesium alloys of my invention may beactivated with pure water since the lithium hydroxide formed is solubleand, therefore, provides a good conducting elec- In the appended claimsthe term water unless specified to be pure refers to natural waters suchas sea water containing enough dissolved salts to make themelectrolytes.

I have found the alloys of my invention particularly useful where veryhigh drains and short come-up time are desirable. The alloys of myinvention like magnesium acquire a coating on exposure to air, and thiscoating must be removed before the full voltage of the cell is obtained.

Therefore, when high drain and short come-up time is desired I use anelectrolyte other than ordinary water. Dilute acid is highly effective.I have found, for example, that in a cell composed of a 60%magnesium-lithium alloy and silver chloride that the adding of a reserveelectrolyte of 5% H2SO4 provides a voltage of 1.60 at 0.8 amperes persquare inch and a come-up time of only a few hundredths of asecond.

,The examples of the applications of the electrode of this invention toprimary cells are illustrative only. Other uses of the electrodes ofthis invention will be evident to those familiar with the art. Theinvention is accordingly not limited to the examples given but only bythe appended claims.

What I claim is:

1. An electrode for electrical systems having an electrochemicalpotential within 0.8 v. as elec tropositive as lithium and a rate ofattack by Water less than one-tenth that of lithium, said 4 electrodebeing formed of an alloy of magnesium and lithium containing 7 52-70%magnesium.

2. A primary cell consisting of an electrode of amagnesium-lithium alloycontaining 5270% magnesium and a depolarizing electrode activated bypure Water. 7

3. A primary cell consisting of an electrode of a magnesium-lithiumalloy containing 52-70%.

magnesium and a depolarizing electrode, activated by a dilute acidsolution.

REGINALD S. DEAN.

REFERENCES CITED 'The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

1. AN ELECTRODE FOR ELECTRICAL SYSTEMS HAVING AN ELECTROCHEMICALPOTENTIAL WITHIN 0.8 V. AS ELECTROPOSITIVE AS LITHIUM AND A RATE OFATTACK BY WATER LESS THAN ONE-TENTH THAT OF LITHIUM, SAID